Calibration in International Units against WHO International Standards

Our VQC-Sanquin standards have also been extensively calibrated in IUs against the first and second WHO international standards by multiple replicate bDNA 3.0 assays. The calibration in IUs by this and other NAT methods was also performed in the first WHO collaborative studies in which the VQC-Sanquin standards have been tested as candidate international standards. The complexities with calibration and stability of lyophilised WHO replacement standards for viral NAT were not fully understood at the time the first WHO standards were established. The calibration studies of the VQC-Sanquin standards against WHO replacement standards have shown significant shifts in the IU values in certain NAT methods and this raises serious doubts about the continuity of the IUs, at least for HIV-1, HCV and parvo B19V. The calibration of a secondary standard for NAT is not a trivial exercise, certainly when another source material or viral nucleic acid sequence is used for the replacement standard. Therefore most laboratories do not use the WHO standard for calibration of their own in house secondary standard, but rather directly use the primary WHO standard for validation or calibration of their NAT system. Significant shifts in IU values were reported by the commercial NAT systems when testing the 3rd International Standard for parvo B19V. The manufacturers of HIV viral load assays report their quantitative results in copies/mL rather than in IU/mL. Because of stability issues with the 3rd and 4th WHO HCV standards the VQC-Sanquin standard has been used as an alternative for NAT validation so that the original analytical sensitivity claims (95% and 50% LOD in IU/mL) of the NAT manufacturer could be confirmed.

Read more about the calibration of the native VQC-Sanquin and inactivated BQC standards in IU/mL in this validation report (PDF).